Patent GB-717113-A (GB)
Title: Improvements in magnetic recording apparatus
Inventor: DEAN JAMES
IPC: G11B19/22
Filed: 1949-11-28
Abstract: 717,113. Recording-apparatus ; digital etectric calculating-apparatus. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Nov. 16, 1950 [Nov: 28, 1949], No. 30495/49. Classes 106 (1) and 106 (4). [Also in Group XXXV] Apparatus for the magnetic recording of electric signals comprises a drum carrying a magnetic recording medium upon its outer peripheral surface and rotatable about a fixed central shaft passing axially therethrough, a first electric motor for driving the drum and a second electric motor for operation as a variable braking device for the drum, each of the motors being housed within the drum and each having its rotor elements carried by the drum and its stator elements secured to the shaft. A drum 6, closed by end frames 9, 10, is rotatably mounted on a fixed central shaft 1 supported in a vertical position by the upper end plate 28 of a casing 7 comprising four columns 29 merging in a lower flange 30 secured to a massive base 8. The drum 6 is rotated by an electric motor 38 comprising a stator 2 and rotor 3 while synchronism with a series of signals to be recorded is maintained by means of a braking motor 39 comprising a stator 4 and rotor 5. The drum 6 is of non-magnetic material;' preferably formed of bronze centrifugally cast and accurately machined and provided with an electroplated layer of nickel round its curved outer surface. The end frames 9, 10, which may be machined castings of non-magnetic metal, e.g. bronze, are fastened by screws 27 to the drum 6 and each is formed with a re-entrant portion 36 axially bored at 41 to receive the rotors 3, 5 which may be clamped against shoulders by screw rings 25 26. The stator 2 may comprise a three-phase winding on a laminated iron core and the stator 4 a single phase winding while the rotors 3, 5 comprise annular structures with squirrel cage windings. The simple phase winding is energized from a suitable source of braking current controlled to maintain the required synchronism. The rotatable drum structure is supported on the fixed shaft 1 at its lower end by opposed thrust ball races 11, 12 externally a tight fit within a bore 42 of the end frame 9 and internally a tight fit on the shaft 1, the races being retained by a cap 43 serving to locate the drum axially. The drum is supported at its upper end by a plain ball race 13 which is a heat fit on the shaft 1 and allows for slight axial-displacement due to differential expansion of drum and shaft. The lower end of the shaft 1 is rigidly clamped to the base 8 by means of a taper collet 32 m a bore 44 in a bushing 45 bolted to the base, the collet being secured and adjusted by a nut 33 screwed to the end of the shaft 1 and locked by means such as the clamping screw and slot shown. The upper end of the shaft 1 is a push fit in a bushing 34 held in the upper end plate 28, thus allowing for differential expansion. Oil is retained in lower and upper bearings by the provision of slots and recesses 14, 15 which each form a labyrinth type packing and by the provision of grease grooves 16, 17 and 18. The casing 7 is accurately positioned with respect to the base 8 by a spigot 23 entering a recess 37 and is secured by bolts. The leads for the two motors are conveyed from an external plug 24 in the base to the stators through a channel 19, and through guide tubes 21, 22 and channel 20. The four columns 29 of the casing 7 are situated at 90 degrees circumferential spacings and flat faces thereof are accurately machined with respect to the locating bushes in the base so that magnetic recording and reproducing heads mounted thereon for presentation to the recording surface are parallel thereto. The apparatus is designed to have a high moment of inertia to friction ratio of the rotating parts and the mounting of the motors within the drum and between its bearings minimizes errors due to torsion of the shaft. The apparatus is particularly suitable for storing data in digital electric calculating apparatus. Specifications 707,635 and 707,637 are referred to.